1. Field of the Invention
The present invention relates generally to methods, systems and apparatus for determining the position or location of vehicles in a transit network and, in particular, to a system and method for determining the location or position of a train or locomotive in a track network made up of multiple interconnected tracks, where wayside (signal system) devices are placed or positioned throughout the track network and associated with the specific portions or blocks of track over which the train traverses.
2. Description of Related Art
Train control systems provide many advantages to controlling, monitoring and tracking trains traversing tracks in a track network. For example, such train control systems provide protection against train-to-train collisions, protection against overspeed derailments, as well as protection against collisions between trains, equipment, personnel, vehicles and other objects. In order to provide such protection, the train control system must obtain data and information about the location of the various trains in the network, work crews, sections of track that have operating speeds below maximum track speed, etc. Such data is made available to the train control system normally through a combination of an on-board track database, as well as radio communications through which other train locations and dynamic information, e.g., temporary speed restrictions, switch alignment, etc., is conveyed. Knowing the restrictions in front of the train is an important part of the equation for providing protection, and additionally, the present location or position of the train is required to make important control decisions.
According to the prior art, current navigation systems are available and used for train control. For example, such existing systems use a combination of a positioning system, e.g., a Global Positioning System (GPS), and tachometer speed. This combination provides a general location of the train, but cannot provide the resolution required to differentiate between adjacent tracks with the degree of certainty required to safely navigate in areas of parallel tracks, or multiple tracks in a specified and identified area.
Various methods exist to augment navigation in order to distinguish between one track and another. One such method includes monitoring switch position, e.g., normal or reserve, and transmitting that information to the locomotive in order to determine the route that will be taken through a switch. Another method includes the use of inertial sensors to determine yaw of the locomotive, with software to translate that information and data into movement through a switch. Yet another method is implemented through the use of transponders affixed to the rail bed with readers on each locomotive to interrogate those transponders, and determine which path has been taken through a switch.
Each of the above-referenced methods provides some functionality, but each also realizes various hazards and deficiencies, which would result in an incorrect determination of the train route through a switch. For example, if a switch monitor or radio interface is non-functional, the train control system will need to rely upon an operator to instruct the system as to which route was taken. This is also true with the transponder solution, if a tag or reader is damaged. In addition, potential errors exist with inertial navigation systems that make them ineffective in determining a route through a switch, such as long turnouts with little deviation, or switches located on curved track, where both the normal and reverse paths result in some angular deflection.
Another drawback that exists is the precision of a GPS or navigational system. While such a navigational or positioning system is capable of providing a fairly granular estimation of the train location, what is provided is a roughly circular area that provides only an estimated position of an object, in this case a train. However, this circular area or estimated position provides a location where the object or train can be anywhere within the circle. Such error is known in the railroad industry as cross track error and requires the additional functions discussed above in order to ensure appropriate positioning data as obtained or calculated.
As discussed above, various existing methods and systems are available in order to estimate train location in a track network. For example, one or more of the following patents/publications describe train control systems or functions that have some positioning ability: U.S. Publication No. 2006/0271291 to Meyer; U.S. Pat. No. 7,142,982 to Hickenlooper et al.; U.S. Publication No. 2006/0253233 to Metzger; U.S. Pat. No. 7,079,926 to Kane et al.; U.S. Pat. No. 6,996,461 to Kane et al.; U.S. Publication No. 2005/0065726 to Meyer et al.; U.S. Pat. No. 6,865,454 to Kane et al.; U.S. Pat. No. 6,641,090 to Meyer; U.S. Pat. No. 6,480,766 to Hawthorne et al.; U.S. Pat. No. 6,456,937 to Doner et al.; U.S. Pat. No. 6,374,184 to Zahm et al.; U.S. Pat. No. 6,373,403 to Korver et al.; U.S. Pat. No. 6,360,998 to Halvorson et al.; U.S. Pat. No. 6,311,109 to Hawthorne et al.; U.S. Pat. No. 6,218,961 to Gross et al.; and U.S. Pat. No. 5,129,605 to Burns et al.
As discussed, the various prior art systems and methods exhibit certain drawbacks and deficiencies. In addition, many of these solutions and systems are amenable to further augmentation or beneficial functioning in order to provide greater confidence that the overall navigational system has determined the correct path and location of the train. In addition, and when it comes to safety on and along the tracks in a track network, additional validation and determination of exact train location is of the utmost importance.